Feedback modulates gamma oscillations in a hypothesis testing paradigm

We analyzed the time-varying modulation of gamma (>30 Hz) electroencephalographic (EEG) activity exerted by positive and negative feedback in a hypothesis testing paradigm. Ten college students serially tested hypotheses concerning a hidden rule by judging its presence or absence in triplets of digits and revised them on the basis of an exogenous performance feedback. The EEG signal was convolved with a family of complex wavelets and brain potentials were extracted in the gamma range. Feedback-related modulations were found as early as 100 ms after feedback onset, as well as in the 300-600 ms time-window. The results were discussed in terms of functional and neurophysiological models of feedback.

Modulation of late alpha band oscillations by feedback in a hypothesis testing paradigm

We used the electroencephalogram (EEG) to investigate whether positive and negative performance feedbacks differentially modulate late time-locked oscillatory brain activity in hypothesis testing. Ten college students serially tested hypotheses concerning a hidden rule by judging its presence or absence in triplets of digits, and revised them on the basis of an exogenous performance feedback. The EEG signal was convolved with a family of complex wavelets and induced brain potentials were extracted in the alpha range (8-13 Hz). The time-varying modulation of alpha activity time-locked to positive and negative feedback was analyzed in the 350-700 ms time-window. The results showed differential feedback-induced modulations of upper-alpha rhythms (> or =10 Hz) between 450 and 700 ms in parieto-occipital and central regions, and of lower-alpha rhythms (<10 Hz) between 350 and 450 ms in central regions. These results were interpreted in terms of differential functional roles of feedback in short-term memory and active inhibition/disinhibition of resources for subsequent hypothesis testing. Some implications for cognitive models of feedback are discussed.

Time-frequency intracranial source localization of feedback-related EEG activity in hypothesis testing

The neural correlates of the response to performance feedback have been the object of numerous neuroimaging studies. However, the precise timing and functional meaning of the resulting activations are poorly understood. We studied the electroencephalographic response time locked to positive and negative performance feedback in a hypothesis testing paradigm. The signal was convoluted with a family of complex wavelets. Intracranial sources of activity at various narrow-band frequencies were estimated in the 100- to 400-ms time window following feedback onset. Positive and negative feedback were associated to 1) early parahippocampo-cingular sources of alpha oscillations, more posteriorly located and long lasting for negative feedback and to 2) late partially overlapping neural circuits comprising regions in prefrontal, cingular, and temporal cortices but operating at feedback-specific latencies and frequencies. The results were interpreted in the light of neurophysiological models of feedback and were used to discuss methodological issues in the study of high-level cognitive functions, including reasoning and decision making.

Non-linear forecasting measurements of multichannel EEG dynamics

This work presents a new method for studying the underlying dynamics of multichannel EEG on the basis of the mathematical theory of dynamical systems. It computes the local loss of predictability and Kolmogorov entropy of the dynamics reconstructed from brain electrical activity. This reconstruction uses multichannel recordings in order to quantify an equivalent of spatio-temporal mapping. Five experimental conditions have been studied: closed eyes at rest, closed eyes and counting even numbers, staring at a spotlight, passive and active auditive odd-ball tasks. The entropy is positive for all the experimental conditions which proves that the underlying EEG dynamics are chaotic. Moreover, on the basis of the dynamical signature it is possible to differentiate 3 types of EEG activity: the rest closed eyes activity, the task closed eyes activity (counting and odd-ball tasks) and the open eyes activity (staring at a spotlight). It is inferred that this index could characterize task-related changes in brain activity.

[Evoked potentials and vigilance states induced during the course of choice reaction time tests]

Characteristics of Visual Evoked Potentials (N120, P200, P300) were investigated during choice reaction time situations in a group of 10 subjects practising meditation (E.S.) versus a matched control group (C.S.) During a series of visual stimuli occuring at fixed intervals, with 10% random omissions, the subjects were asked : 1) to respond by a finger displacement to each visual stimulus; 2) to hold on the response to the stimulus and to respond to omission. Both tasks were recorded before and after the practice of meditation or rest for the controls. The intergroup comparison showed that the experimental subjects had faster RT's with less mistakes, and N120 and P200 of larger amplitude and shorter latency. These differencies were significant before and after meditation. The transient effects of meditation or rest, were opposite for the two groups : whereas after meditation the RT's became longer with less mistakes, and the amplitude of P300 larger, after rest there was a decrease of the P300 amplitude and no change in the RT's of the controls. These results are interpreted in terms of selective attention capacity and information processing strategies, A.S.C. being used as a model for the study of these processes.